Pro PHP Security

The global accessibility of websites is a double-edged sword: At the same time that your online e-commerce site is open for business to anyone with an Internet connection, it is also open to malicious attack. websites based upon the popular language PHP, are no exception. Thus, it is both astonishing and worrisome that there are currently so few books devoted to PHP security — particularly ones that go beyond the handful of typical security countermeasures discussed in articles. Fortunately, Pro PHP Security, written by Chris Snyder and Michael Southwell, is intended to fill this critical need.

Published by Apress on 8 September 2005, with the ISBN 978-1590595084, Pro PHP Security spans 528 pages, consisting of 24 chapters organized into four major parts. The first part, comprising only one chapter, explains the nature and significance of computer security, and reasons as to why absolute security is an unattainable goal. Nonetheless, it is worthwhile to take all appropriate and reasonable security measures, and the authors provide a brief overview of the different types of attacks to which Web applications are vulnerable.

On their website, Apress has a page devoted to the book, where they offer the book's source code (in a Zip archive file), the table of contents, corrections to the book (i.e., errata), and a sample chapter (Chapter 12 - Preventing SQL Injection) in PDF format. In addition, there is a link for any reader who would like to purchase this title as an e-book.

One of the most laudable aspects of Pro PHP Security, is that the authors — both experienced software and website developers — go far beyond the standard PHP security advice of validating and escaping user input, etc. Those topics are covered in depth, but they are provided in the context of thorough discussions as to how to set up a secure environment in which to use those techniques. In addition, the authors present best practices that have evolved over time, as Web masters and system administrators have learned — often the hard way — the general types of attacks to which their websites and computer networks have been subjected.

In fact, Snyder and Southwell hold off on presenting the aforesaid specific PHP security techniques, until the third part of the book. Prior to that, they explain the characteristics of a secure online computing environment, such as using encryption, securing network connections via SSL and SSH, controlling access via authentication and permissions, and other important topics. Their coverage of the subject matter is complete, without being overwhelming. For instance, the material on encryption is helpfully divided into two separate chapters — devoted to theory and practice, respectively. Consequently, a PHP application developer or system administrator can immediately dive into the authors' recommended practices for encoding sensitive data, without getting bogged down in the theoretical underpinnings, if the reader is in a hurry to implement encryption on their own systems, or simply has no interest in the theory behind the methods.

As noted earlier, Part 3 of this monograph explains all of the well-known techniques that crackers use for attacking PHP-based websites, as well as the countermeasures that should be adopted by the developer or maintainer of the site. First up is validation of user input, which — though being essential to basic security — is still neglected on far too many websites. The attention to detail seen in this discussion is also reflected in the subsequent chapters, which cover SQL injection, cross-site scripting, remote execution, temporary files, and session hijacking. For each topic, the authors explain how the typical attack is attempted, and what needs to be done to prevent such attacks.

The fourth and last major part of the book covers vitally important topics that are usually glossed over in most PHP security books, or neglected altogether. Snyder and Southwell explain methods of limiting access to your website to humans (thus minimizing attacks that employ scripts), verifying the identities of those users, authorizing what those users can do on your system, and tracking their actions once they have logged in. The authors also explain how to reduce the chances of data loss, and how to execute system commands and make remote procedure calls without exposing your site to vulnerabilities. The last chapter covers the benefits to be gained from opening up your site and its source code to a review by your technical peers.

This book has much to recommend it: The discussions of security issues are more complete and thorough than in any other book that I have seen. The information chosen by the authors is detailed enough to be understandable and usable, but not so excessive as to prove daunting or discouraging to the reader who needs answers to their security questions, and does not have the time or inclination to slog through academic or pointless discussion. The information is well-organized, and presented in context, so the reader is not simply given a laundry list of security techniques, but instead better understands the rationale behind them. Lastly, because no technical topic can be covered in full in a single book, the authors provide a generous number of references to outside resources.

The content of this book appears to have only one noticeable weakness, and that is the poor quality of the comments in the sample source code. Not only are they few in number and lacking in detail, but they are written in all lowercase letters, with little to no punctuation. This coding style results in the comments visually blending in with the code itself, and makes reading both to be more difficult than is justifiable.

The physical book itself also has only one weakness, and that may only apply to a portion of the copies produced and distributed by the publisher. Specifically, the bottom and side edges of the book are cut cleanly, while the top edge is quite rough. As I was unable to find any mention within the book as to a possible reason or advantage for having the rough edging on top of the pages, I can only conclude that it was not intended on the part of Apress, and represents an error in production. I hope that the copy that I received — kindly given to me by the publisher — is not representative of all the copies produced and sold.

In spite of these minor complaints, I was quite pleased with this book. Pro PHP Security is arguably the most comprehensive PHP security book available, and is highly recommended to any developer or administrator of a PHP-based website.